<html>
  <head>
    <style>
      body {
        margin: 0;
      }
      .outerContainer {
        display: flex;
        height: 100px;
        background-color: red;
      }
      .innerContainer {
        display: flex;
        flex: 1;
        background-color: lime;
      }
    </style>
  </head>
  <body>
    <div class="outerContainer">
      <div class="innerContainer"></div>
    </div>
  </body>
</html>
